(a) Field of the Invention
This invention relates to a method of non-destructively identifying different kinds of rolled steel for structural purposes or like materials.
(b) Prior Art
Prior art methods of identifying different kinds of steel include one, in which mechanical properties of steel is determined from tensile tests and bending tests on test pieces, and one, in which chemical compositions of steel are determined by analytic tests on test samples. Usually, different kinds of steel are identified from certificates (mill sheets), on which the results of tests noted above are described, and also marks provided on steel. Therefore, it has been impossible to identify the kind of steel without any identification mark and after machining and assembly of steel.
Different kinds of steel cannot be identified by visual inspection. As a non-destructive method of identification, there is a spark test method. This method is standardized in Japan as spark test method for JIS G 0566 steel. To conduct this test, a light shield screen or partition member or a movable dark box is necessary for the purposes of preventing effects of wind and adjusting the brightness, under which the test is conducted. This method is effective for estimating different kinds of carbon steel for structural purposes containing carbon in a wide range from below 0.1% to above 0.6% and also stainless steel and other special alloy steel containing chromium, nickel, molybdenum, tungsten, etc. With this method, however, it is very difficult to identify different kinds of rolled steel for structural purposes. This is so because any structural rolled steel contains substantially an equal amount (i.e., 0.12 to 0.22%) of carbon. Especially, broadly used kinds of steel ASTM A 36 (which is referred to as SS41 in Japan) and ASTM A 573 (which is referred to as SM50 in Japan) are distinguished from each other in terms of the difference in the contents of silicon and manganese which can be hardly discriminated by the spark test.